Physiology 3120 Lecture Notes - Lecture 10: Cardiac Muscle, Circulatory System, Arteriole

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Physiology 3120
Dr. Stavraky
Lecture 10
CV Regulatory Mechanisms
Mechanisms for the control of circulation:
(i) Local Mechanisms (autoregulation)
1. Myogenic theory
2. Metabolic theory
(ii) Humoral Mechanism s
1. Vasoconstrictors (increase MAP)
2. Vasodilators (decrease MAP)
(iii) Neural Mechanisms (ANS)
- Cholinergic decrease MAP
- Adrenergic increase MAP
- Some of the effects of the ANS on the cardiovascular system:
- SNS can also cause contraction of the veins to increase venous return to increase EDV to
increase SV to increase MAP (not shown in diagram)
- Note: CM = cardiac muscle, SM = skeletal muscle
The Baroreceptor Reflex:
- homeostatic mechanism (neg feedback)
- if your BP is too low, you would pass out bc the blood flow to your brain is too low
- if your BP is too high, it can cause cardiovascular disease
- maintains normal mean arterial pressure for proper perfusion of tissues throughout the body
- involves rapid adjustments to both cardiac output and total peripheral resistance
Heart and Blood Vessels
- heart is regulating CO and your blood vessels are regulating TPR to maintain MAP
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Baroreceptor Reflex
- relies on specialized structures:
o mechanoreceptors (2 types):
higher pressure baroreceptors
located in aortic arch and carotid sinuses
involved in the baroreceptor reflex
low pressure volume receptors
not involved in baroreceptor reflex
o CV control center
Located in the medulla in the brainstem
This is the control center in the negative feedback system
Receives info from the receptors and makes sure the info from the receptor
match the setpoint and if it doesn’t, it causes a change in CO or TPR to maintain
MAP
High Pressure Baroreceptor
- Located in the walls (tunica externa) of:
o the aortic arch
o the carotid sinus
- Stretch sensitive receptors constantly monitor changes in arterial pressure and
constantly relay info to CV center (there is a tonic release of info being sent to the
CV even when MAP is at the proper level)
- Increased BP stretches walls of blood vessels increase AP firing rate by the
baroreceptors signals sent to CV center (and vice versa)
Low Pressure Volume Receptors
- Not involved in baroreceptor reflex they are involved in other things like
cardiovascular control regulatory mechanisms
- Located in left and right atrium
o predominantly the right atrium bc that’s where the venous side circulation
is and the venous side of the circulation contains majority of the blood and
if these are volume receptors, they want to be where most of the blood is
contained
- Detect fullness of circulation
- Help regulate blood volume
- Blood pressure is related to blood volume: The higher the blood volume the
higher the MAP (and vice versa)
2 Scenarios where these low pressure volume receptors function:
- Dehydration Drop in blood volume (drop in MAP) release of ADH (helps retain water from
urine and causes vasoconstriction in high concentrations) renin release formation of Ang II
(powerful vasoconstrictor) Ang II also stimulates thirst
- Increase in blood volume (increase in MAP) decrease in ADH, renin, Ang II Increases Atrial
Natriuretic Factor (humoral vasodilator)
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Baroreceptor Reflex
- Within the walls of the aortic arch and carotid sinuses we have baroreceptors (high pressure
baroreceptors involved in the baroreceptor reflex)
- These baroreceptors have nerves going to the CV center (in medulla) to send signals
- So nerves that originate in the aortic baroreceptors are going to travel back to the medulla
through the vagus nerve
- The carotid sinus baroreceptors send signals back to the medulla through the carotid sinus
nerve
- The dash and solid lines means that they could be both myelinated and unmyelinated fibers (but
that’s not really important)
- CV center looks at the signals and compares it to the setpoint and sends signals to the various
target organs (one of which is the heart)
- In terms of PSYN output, the PSYN nerve that innervates the heart is the vagus nerve (so the
vagus nerve conveys both efferent and afferent information)
- Vagus nerve innervates the SA node, AV node and the cardiac contractile cells (to some extent)
- Vagus nerve releases ACh which is going to decrease HR and decrease the force of contraction
- SYN nerves first travel down the spinal cord
- eventually the preganglionic sympathetic fibers will exit the spinal cord and synapse in the
sympathetic ganglion
- then the postganglionic fibers are going to travel to the heart to innervate the SA node, AV node,
and cardiac contractile cells to release NE which will increase HR and increase force of
contraction
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Document Summary

Mechanisms for the control of circulation: (i) local mechanisms (autoregulation: myogenic theory, metabolic theory (ii) humoral mechanism s, vasoconstrictors (increase map, vasodilators (decrease map) (iii) neural mechanisms (ans) Some of the effects of the ans on the cardiovascular system: Sns can also cause contraction of the veins to increase venous return to increase edv to increase sv to increase map (not shown in diagram) Note: cm = cardiac muscle, sm = skeletal muscle. The baroreceptor reflex: if your bp is too low, you would pass out bc the blood flow to your brain is too low if your bp is too high, it can cause cardiovascular disease. Maintains normal mean arterial pressure for proper perfusion of tissues throughout the body involves rapid adjustments to both cardiac output and total peripheral resistance. Heart is regulating co and your blood vessels are regulating tpr to maintain map. Located in the walls (tunica externa) of: the aortic arch the carotid sinus.

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